Preassembled drive means units are known in the prior art and are used e.g. for control chains of internal combustion engines. DE-OS 3 909 458 discloses e.g. a sprocket-retaining and chain-guide element for a control chain in the case of which arcuate grooves are provided for loosely accommodating the sprockets and the control chain. A groove for accommodating a sprocket is formed by a releasable plate and the sprocket-retaining and chain-guide element. In addition, one embodiment shows the sprocket-retaining and chain-guide element together with a pivotably supported chain tensioning means which is tensioned with the aid of a compression spring.
Another preassembled drive means unit is described in U.S. Pat. No. 4,879,977. In this device two gears are held in position by a suitably shaped guide plate. In order to permit the gears to be arranged in respective openings provided in the guide plate, the chain must be still open. When the gears have been inserted in the respective openings, the chain is put round the gears and closed.
It is, for example, also possible to implement the support body as a multi-part component, as has been done in the case of the devices according to U.S. Pat. No. 4,869,709 or EP-A-0 280 365, so that the drive means wheels can also be arranged in a condition in which the endless drive means has already been put around them.
EP-A-0 848 139 discloses a preassembled traction means drive unit comprising an integral support body. In the case of this preassembled traction means drive unit, the traction means wheels, with the traction means put around them, are positioned for mounting in holding pockets and fixed by means of a locking element formed integrally with a holding device.
After having been assembled, the above-mentioned preassembled drive means units including the support body remain on a drive unit, especially an engine block of an internal combustion engine. The embodiments of the drive means unit mainly aim at permitting the drive means wheels and the endless drive means to be preassembled. Specific components of the drive means unit fulfil functions assigned thereto, both during the main assembly as well as during the future use at the drive unit. Other components and functions become completely unimportant when the unit is operated later on. The various tasks resulting from the assembly and the future use lead—especially with respect to the use of the preassembled drive means unit in the field of automobile industry, the high number of pieces existing in this field of industry and the increasing degree of automation—to a constant demand for improvements and a necessary adaptation to higher demands.